1. Field of the Invention
The disclosed embodiments of the present invention relate to a calibration method for a communication system, associated circuits and a non-transitory machine readable medium, and more particularly, to a pre-distortion method for compensating a power amplifier of a radio frequency (RF) circuit having non-linear characteristics and/or memory effect, an associated apparatus and a non-transitory machine readable medium.
2. Description of the Prior Art
Spectral efficiency is becoming a more significant issue in the field of mobile communication as a result of wider bandwidth requirements along with rapid development of the technology. In a complex non-constant envelope modulation, circuit designers have to grasp characteristics of a power amplifier employed in an RF circuit due to high peak-to-power ratio (PAPR). FIG. 1 is a diagram illustrating a transmitter of a conventional wireless communication system. Non-linear characteristics of a power amplifier 104 may produce amplitude modulation-amplitude modulation (AM-AM) distortion and amplitude modulation-phase modulation (AM-PM) distortion at an output terminal. The distortion becomes worse as the bandwidth becomes wider, which causes out-of-band spectral re-growth and in-band distortion effects. Eventually, the error vector magnitude (EVM) may be degraded. In addition, the output of the power amplifier 104 may be affected by past input, which is known as the memory effect. The memory effect deteriorates as the bandwidth becomes higher. A conventional pre-distortion circuit 102 cannot handle the non-linear characteristics/memory effect of the baseband circuit, and therefore may have difficulty satisfying requirements of modern wireless communication systems.